crypto/ec/ecdh_ossl.c

   1 /*
   2  * Copyright 2002-2018 The OpenSSL Project Authors. All Rights Reserved.
   3  * Copyright (c) 2002, Oracle and/or its affiliates. All rights reserved
   4  *
   5  * Licensed under the Apache License 2.0 (the "License").  You may not use
   6  * this file except in compliance with the License.  You can obtain a copy
   7  * in the file LICENSE in the source distribution or at
   8  * https://www.openssl.org/source/license.html
   9  */
  10
  11 /*
  12  * ECDH low level APIs are deprecated for public use, but still ok for
  13  * internal use.
  14  */
  15 #include "internal/deprecated.h"
  16
  17 #include <string.h>
  18 #include <limits.h>
  19
  20 #include "internal/cryptlib.h"
  21
  22 #include <openssl/err.h>
  23 #include <openssl/bn.h>
  24 #include <openssl/objects.h>
  25 #include <openssl/ec.h>
  26 #include "ec_local.h"
  27
  28 int ossl_ecdh_compute_key(unsigned char **psec, size_t *pseclen,
  29                           const EC_POINT *pub_key, const EC_KEY *ecdh)
  30 {
  31     if (ecdh->group->meth->ecdh_compute_key == NULL) {
  32         ECerr(EC_F_OSSL_ECDH_COMPUTE_KEY, EC_R_CURVE_DOES_NOT_SUPPORT_ECDH);
  33         return 0;
  34     }
  35
  36     return ecdh->group->meth->ecdh_compute_key(psec, pseclen, pub_key, ecdh);
  37 }
  38
  39 /*-
  40  * This implementation is based on the following primitives in the
  41  * IEEE 1363 standard:
  42  *  - ECKAS-DH1
  43  *  - ECSVDP-DH
  44  *
  45  * It also conforms to SP800-56A r3
  46  * See Section 5.7.1.2 "Elliptic Curve Cryptography Cofactor Diffie-Hellman
  47  * (ECC CDH) Primitive:". The steps listed below refer to SP800-56A.
  48  */
  49 int ecdh_simple_compute_key(unsigned char **pout, size_t *poutlen,
  50                             const EC_POINT *pub_key, const EC_KEY *ecdh)
  51 {
  52     BN_CTX *ctx;
  53     EC_POINT *tmp = NULL;
  54     BIGNUM *x = NULL;
  55     const BIGNUM *priv_key;
  56     const EC_GROUP *group;
  57     int ret = 0;
  58     size_t buflen, len;
  59     unsigned char *buf = NULL;
  60
  61     if ((ctx = BN_CTX_new_ex(ecdh->libctx)) == NULL)
  62         goto err;
  63     BN_CTX_start(ctx);
  64     x = BN_CTX_get(ctx);
  65     if (x == NULL) {
  66         ECerr(EC_F_ECDH_SIMPLE_COMPUTE_KEY, ERR_R_MALLOC_FAILURE);
  67         goto err;
  68     }
  69
  70     priv_key = EC_KEY_get0_private_key(ecdh);
  71     if (priv_key == NULL) {
  72         ECerr(EC_F_ECDH_SIMPLE_COMPUTE_KEY, EC_R_MISSING_PRIVATE_KEY);
  73         goto err;
  74     }
  75
  76     group = EC_KEY_get0_group(ecdh);
  77
  78     /*
  79      * Step(1) - Compute the point tmp = cofactor * owners_private_key
  80      *                                   * peer_public_key.
  81      */
  82     if (EC_KEY_get_flags(ecdh) & EC_FLAG_COFACTOR_ECDH) {
  83         if (!EC_GROUP_get_cofactor(group, x, NULL) ||
  84             !BN_mul(x, x, priv_key, ctx)) {
  85             ECerr(EC_F_ECDH_SIMPLE_COMPUTE_KEY, ERR_R_MALLOC_FAILURE);
  86             goto err;
  87         }
  88         priv_key = x;
  89     }
  90
  91     if ((tmp = EC_POINT_new(group)) == NULL) {
  92         ECerr(EC_F_ECDH_SIMPLE_COMPUTE_KEY, ERR_R_MALLOC_FAILURE);
  93         goto err;
  94     }
  95
  96     if (!EC_POINT_mul(group, tmp, NULL, pub_key, priv_key, ctx)) {
  97         ECerr(EC_F_ECDH_SIMPLE_COMPUTE_KEY, EC_R_POINT_ARITHMETIC_FAILURE);
  98         goto err;
  99     }
 100
 101     /*
 102      * Step(2) : If point tmp is at infinity then clear intermediate values and
 103      * exit. Note: getting affine coordinates returns 0 if point is at infinity.
 104      * Step(3a) : Get x-coordinate of point x = tmp.x
 105      */
 106     if (!EC_POINT_get_affine_coordinates(group, tmp, x, NULL, ctx)) {
 107         ECerr(EC_F_ECDH_SIMPLE_COMPUTE_KEY, EC_R_POINT_ARITHMETIC_FAILURE);
 108         goto err;
 109     }
 110
 111     /*
 112      * Step(3b) : convert x to a byte string, using the field-element-to-byte
 113      * string conversion routine defined in Appendix C.2
 114      */
 115     buflen = (EC_GROUP_get_degree(group) + 7) / 8;
 116     len = BN_num_bytes(x);
 117     if (len > buflen) {
 118         ECerr(EC_F_ECDH_SIMPLE_COMPUTE_KEY, ERR_R_INTERNAL_ERROR);
 119         goto err;
 120     }
 121     if ((buf = OPENSSL_malloc(buflen)) == NULL) {
 122         ECerr(EC_F_ECDH_SIMPLE_COMPUTE_KEY, ERR_R_MALLOC_FAILURE);
 123         goto err;
 124     }
 125
 126     memset(buf, 0, buflen - len);
 127     if (len != (size_t)BN_bn2bin(x, buf + buflen - len)) {
 128         ECerr(EC_F_ECDH_SIMPLE_COMPUTE_KEY, ERR_R_BN_LIB);
 129         goto err;
 130     }
 131
 132     *pout = buf;
 133     *poutlen = buflen;
 134     buf = NULL;
 135
 136     ret = 1;
 137
 138  err:
 139     /* Step(4) : Destroy all intermediate calculations */
 140     BN_clear(x);
 141     EC_POINT_clear_free(tmp);
 142     BN_CTX_end(ctx);
 143     BN_CTX_free(ctx);
 144     OPENSSL_free(buf);
 145     return ret;
 146 }